Circulating concentrating evaporation for caustic regeneration



1966 w. K. ROBBINS ETAL 3,228,754

CIRCULATING CONCENTRATING EVAPORATION FOR CAUSTIC REGENERATION OriginalFiled July 28. 1961 ACID-FREE CATALYTIC HEATING oIL TEMP. 30

CONTROL MERCAPTANS 8 WATER 04 i I I28 I I SCRUBBER N8 k STEAM I\I-SEPARATOR I ORGANIC I25 ACID [9-0 I20 I I CATALYTIC I HEATING oIL I22I LEVEL H2 l CONTROL 46 EVAPORATORV L 'I I02 0 Il6 I32 I CONDENSATE II4I60 SEPARATOR IOGI- I08 44 I52 MAKE-UP P 7 NAOH NAOH BLEED F I G IINVENTORS.

WILLIAM K. ROBBINS,

BY JAMES I SCOTT fl' hw ATTORNEY.

United States l atent O 3,228,754 CIRCULATING CQNCENTRATING EVAPORATIONFOR CAUSTIC REGENERATION William K. Robbins and James 0. Scott, Baytown,Tex., assignors, by mesne assignments, to Esso Research and EngineeringCompany, Elizabeth, N.J., a corporation of Delaware Original applicationJuly 28, 1961, Ser. No. 127,527. Divided and this application Oct. 22,1962, Ser. No. 232,067

1 Claim. (Cl. 23276) This application is a division of copendingapplication Serial No. 127,527, filed July 28, 1961.

The present invention relates to the reconcentration and regeneration ofsolutions of alkali metal hydroxides which have been used to removeorganic acids and mercaptans from flowing hydrocarbon streams. Moreparticularly, the present invention relates to a method and means forconcurrently concentrating the caustic solution while utilizing thesteam evolved during concentration to strip mercaptans from thesolution. In its more specific aspect, the present invention relates toa means and method of regenerating a sodium hydroxide solution whichcontains dissolved organic acids by concentrating and removingmercaptans from said solution in a first stage and recovering organicacids from said solution in a second stage.

Hydrocarbon streams boiling between about 100 F. and about 800 F. andcontaining mercaptans and organic acids (including phenols andcarboxylic acids) are unsuitable for commercial use because of thecorrosivity of the dissolved contaminants. As a consequence of thiscorrosivity, the product streams must be treated either to remove or toneutralize the effect of these contaminants. One method of removing thecontaminants is by contacting the hydrocarbon stream with a concentratedsolution of the hydroxide of an alkali metal hydroxide such as sodium,potassium or lithium. The use of these hydroxides is effective inremoving the mercaptans, phenols, carboxylic acids and other acidiccontaminants from the flowing stream, but are expensive both in the costof the treating solution as Well as in the costs of disposing of thewaste liquid after the caustic solution has become spent. By thepractice of the present invention, the effective life of such a causticsolution may be extended to a period of several times that experiencedin the manner hitherto utilized. Further, by the practice of the presentinvention, it has been found that although the caustic solutions whichare used in the practice of the present invention are highly viscous,concentrations of the caustic to the desired gravity may be accomplishedat atmospheric pressure. Hitherto it has been considered necessary inreconstituting these highly viscous solutions to use a vacuumevaporation system in order to minimize effects of slugging and bubblingwithin the evaporator. It has further been found by the practice of thepresent invention, that the steam evolved during the reconcentration orevaporation step may be utilized to strip mercaptans from the solution,thereby obviating the preliminary removal of mercaptans beforereconstitution.

During the contacting of the flowing hydrocarbon stream with the causticsolution, the Water which normally occurs in the flowing hydrocarbonstream is also removed along with the contaminants sought to be absorbedby the caustic scrubbing solution. The natural result of the absorbingof this moisture is a constant dilution of the scrubbing caustic. If thecaustic solution is maintained at a gravity above 42 Baum, the organicacids extracted from the hydrocarbon stream may be separated into asupernatant layer by cooling the caustic to a temperature of about 100F, to 150 F, but when the caustic strength falls below 42 Baum,particularly 3,228,754 Patented Jan. 11, 1966 where the caustic strengthis below 40 Baume, the organic acids are completely soluble in thecaustic and will not form the separate layer. Therefore, they cannot bedecanted from the caustic tank and an organic acid buildup occurs whichcauses the caustic to become unusable and spent in a relatively shorttime. They caustic strength is therefore preferably maintained within arange of about 42 to 50 Baum.

The present invention prevents the buildup of organic acids byreconstituting the caustic solution to the desired gravity. Moreover,the practice of the present invention prevents a buildup of mercaptanswithin the caustic solution which also would result in an untimelydeactivation of the caustic solution.

The practice of the present invention may be more particularlyunderstood by a reference to the appended drawings wherein:

FIG. 1 is a general schematic diagram of the scrubbing system; 7

FIG. 2 is a representation of a particular feed nozzle into theevaporator;

FIG. 3 is a plan view of the nozzle taken on lines 3-3 of FIG. 2; and

FIG. 4 is a sectional elevation of the nozzle taken on line 4-4 of FIG.3.

Referring more particularly to FIG. 1, the practice of the presentinvention relates to the treatment of catalytic heating oil, forexample, which is introduced into a scrubber by way of line 102 and isdischarged after contacting with the caustic solution by way of line104. A scrubbing caustic solution, such as sodium hydroxide, isintroduced into the scrubbing tower by way of line 106 and is passeddownwardly through the tower in contact with the flowing hydrocarbonstream to be discharged at the bottom of the tower by way of line 108.During the passage through the scrubbing tower, the caustic solutionabsorbs the mercaptans, phenols, carboxylic acids, other aromatic andparafiinic acids, and water, which are present in the catalytic heatingoil feed stock. Therefore, the caustic solution passed by way of line108 is contaminated with the absorbed acidic and sulfur-containingcompounds as well as being diluted to a gravity somewhat below theoptimum.

The solution is then charged by way of line 108 into an evaporator 110and is passed into the shell 112 of the evaporator in a distributed formby means of a baflle 114 which is arranged above the inlet so that thematerial charged into the evaporator impinges upon the bathe and is welldistributed. The distributed caustic feed is then passed through aseries of tubes 116 and is discharged by way of line 118. During passagethrough tubes 116, the caustic is heated to a temperature of 215 F. to300 F. by means of steam which is introduced by Way of line 120controlled by valve 122 and passes through the steam jacket within theshell 112 to be discharged by way of line 124 as condensate. The causticsoda is maintained within the evaporator at a temperature of about 215F. to 300 F. for a time period sufiicient to evaporate enough water toconcentrate the solution from the operating gravity of about 40 to 43Baum to a gravity of about 45 Baum or higher, preferably about 44 to 48Baum. Also, the time period should be sufiicient to allow the mercaptansto be stripped from the caustic solution and carried into the vaporphase with the evolved steam.

The total effiuent, liquid, gas and vapor, from the evaporator 110 ispassed by way of line 118 into a first separator 126 wherein thevaporous steam and gaseous mercaptans are allowed to pass overhead byway of vapor outlet 128 through condenser 130 for disposal. The liquidis passed from the separator by way of standpipe .tion inlet means.recirculation inlet means having a cross-sectional area 132 and line 134into pump 136, and is discharged from pump 136 by way of line 138, valve140, and cooler 142 into a second separator 144, from whence an organicacid supernatant layer is withdrawn by way of upper liquid phase outlet146 and a reconstituted and regenerated caustic soda solution isdischarged by way of lower liquid phase outlet 148 for recycle by way ofline 150 into line 106 and into the scrubber 100. The caustic may bedischarged intermittently or continuously by way of the caustic bleedline 152, while makeup caustic of 45 to 50 Baum or higher is introducedin offsetting amounts through line 154.

Returning now to the evaporator system proper, it is seen that a line156 interconnects the discharge line 134 from the first separator andthe evaporator 110. This line 156 recirculates a portion of the causticto the evaporator to assure a complete concentration of the caustic andremoval of the mercaptan. The evaporator 110 is provided with an inlet158 for this recycle stream, and the inlet 158 is further provided withan orifice plate or choke plate 160 which provides sufficient pressuredrop to prevent the passage of a portion of the feed which is introduced by way of line 108 into the line 156 to bypass the evaporationsystem. The orifice should be about 1% to of the area of the returnconduit. It should be understood that the recycle stream being rechargedinto the evaporator 110 may be provided with suitable pumping means ifnecessary to provide sufiicient head for the recirculation rate desired.Preferably, however, the recycle is accomplished by relying on thepressure head differential which may be obtained by mounting theseparator 126 at a slightly higher elevation than the evaporator 110,and allowing the evolved steam within the tubes 116 to provide a vaporlift for the solution into the separator 126. Thus, the evaporationsystem can be seen to comprise in combination a vertical-tube heatexchanger having a shell with an upper head and a lower head, and aplurality of vertically disposed tubes enclosed within the shell whichcommunicate with the upper head and lower head. Outlet means areprovided in the upper head, and inlet means for the feed are provided inthe bottom of the lower head, with baffie means within and dependingfrom the lower head positioned in confronting relationship with the feedinlet means. A recirculation inlet is provided in the side of the lowerhead. Separating means are provided for separating vapor and liquidwhich are discharged from the exchanger, having a vapor outlet and astandpipe, with overhead conduit means being employed to connect theoutlet means with the separating means, and with return conduit meansbeing employed for connecting the standpipe with the recircula- A chokeorifice is provided in the 1% to 5% of the area of the return conduit,and means communicating with the standpipe are also provided forwithdrawing a portion of the liquid from the separator.

Referring now to FIG. 2, a particular form of injection nozzle isdisclosed which obviates the necessity of using a choke plate such asthe plate 160 shown in FIG. 1. In the modification of FIG. 2, a feednozzle 200 is shown within an evaporator 210 which is generally similarto that shown in FIG. 1. The recycle inlet 220 shown in FIG. 2 is freeof obstruction, and need not be provided with a choke plate. This isaccomplished by mounting the feed nozzle 200 at a position at least ashigh as the bottom of the recycle inlet pipe, but preferably above thisposition, and in forming the feed nozzle with a generally hemisphericalupper surface with discharge passages extending radially therethrough sothat the feed stream will be directed above the inlet 220.

The structure of the nozzle 200 may better be understood by referring toFIGS. 3 and 4 wherein there is disclosed a plan view and a sectionalelevational view of the nozzle. In particular, referring to FIG. 4, thenozzle 200 is seen to communicate with the feed pipe 240 which containsthe charge stream. Radial passages 250 are formed in the head of thenozzle for directing the feed stream in a direction above the horizontalplane defined by the lower portion of the nozzle indicated by thenumeral 260. Therefore, with the nozzle mounted above the recycle pipe,the vector forces imparted to the feed stream will prevent the freshfeed stock from entering the recycle nozzle.

By the practice of the present invention, caustic consumption has beenreduced over 50%. In the practice of caustic scrubbing of a catalyticheating oil stream without regeneration, an average life span of acaustic solution charged had been established at about five days.

-By utilizing the present invention, the life span of the Catalyticheating oil (30,000 bbls./day) was passed through a caustic scrubber incontact with a total charge of 1,000,000 lbs. of 50 Baum sodiumhydroxide solution (circulated at a rate of 2% to 5% by volumedilutionfrom water in feed decreasing the Baum gravity). The caustic wasrecirculated until the specific gravity reached 40 Baum, at which timethe caustic was discarded and a new caustic charge of 50 Baum specificgravity was injected into the system. Under these conditions, thecaustic consumption of 50 Baum sodium hydroxide was about 2,000 bbls. or520,000 lbs/month.

Example II Utilizing the evaporator system as described in FIG. 1, thecatalytic heating oil (30,000 bbls./day) was passed in contact with atotal charge of 1,000,000 lbs. of caustic soda which was circulated at2% to 5% by volume. The caustic soda solution was reconstituted as setforth in the discussion of the aforesaid figure with mercaptans andorganic acids being removed in accordance with the invention.

By utilizing the practice of the present invention, the causticconsumption is about 800 to 900 bbls./month of 50 Baum caustic orslightly less than 235,000 lbs./ month, less than 50% of the causticconsumption heretofore experienced. Also, during the operation of theevaporator system, 95,000 lbs. of marketable organic steam consumptionon a monthly basis is about 7,000 to 12,000 lbs/hr. (estimatedaverage is8,000 lbs/hr.) of steam, which results in a high, attractive economicadvantage based on the saving of caustic solution. An added advantage isthe lessening of spent caustic solution which must be disposed of.

The nature and practice of the present invention having been set forthin detail, including a preferred manner and best mode of practicing theinvention, what is desired to be protected by Letters Patent should bedetermined only by the appended claim and should not be limited by thespecific examples hereinabove given.

We claim:

An evaporation system comprising, in combination,

a vertical-tube heat exchanger comprising a shell, means for circulatinga heating fluid through said shell, an upper head, a lower head, aplurality of vertically disposed tubes enclosed within said shell andcommunicating with said upper head and said lower head, outlet means insaid upper head, feed in et means .in the bottom of said lower head,bafile means within and depending from said lower head and positioned inconfronting relationship with said feed inlet means, recirculation inletmeans communicating with the side of said lower head,

separating means for separating vapor and liquid discharged from saidexchanger and having a vapor outlet and a standpipe,

overhead conduit means connecting said outlet means with said separatingmeans,

return conduit means connecting said standpipe with said recirculationinlet means,

a choke orifice in said recirculation inlet means, said choke orificehaving a cross-sectional area from 1% to 5% of the area of said returnconduit means,

separator means having an inlet, an upper liquid phase outlet, and alower liquid phase outlet,

conduit means connecting said standpipe with said separator means,

cooling means in said conduit means intermediate said standpipe and saidseparator means,

and pump means for circulating fluid from said standpipe to saidseparator means and through said cooling means.

References Cited by the Examiner UNITED STATES PATENTS 6/1911 Guillaume196-100 2/1917 Trump 23-273 11/1922 Webre 159-27 8/ 1931 Lichtenthaeler159-27 11/1931 Kermer 159-27 1/1934 Burnham 159-27 6/1939 Bonotto202-237 XR 1/ 1949 Beckel 202-204 XR 10/1949 Baumann 159-28 2/1953Toulmin 23-274 XR 1/1963 Sumiya 23-274 XR FOREIGN PATENTS 5/1949 Canada.3/ 1960 Germany. 7/1949 Great Britain.

NORMAN YUDKOFF, Primary Examiner.

